I'm thinking if we are trying to be helpful here, since we're dealing with someone who has never used a jack at all, the main thing to dwell on is safety. Such as making sure the trailer tires are blocked/chocked so the trailer cannot move forward or backward, and for sure, once you start jacking it up, to make darn sure no part of your body is in a place where you can be pinned if/when it falls. I'm betting there are many, many injuries and worse every year from trailers/vehicles falling off jacks, most of which we never hear about. I've seen things fall off jacks. Believe this: when they come down, it's in a big hurry.
Always best to do this jacking while it's still hooked to the tow vehicle, but the OP has said they don't want to do that, so it's going to be dicey.
